CAD tip # 8460:

The standard command DGNIMPORT detects references to external .RSC files and if the respective RSC file is available in the support path, its linetype definitions are converted so that the DGN entities look the same also in the AutoCAD DWG drawing. It is not neccessary to set any mappings in the DGN import dialog - the conversion is automatic. If the requested RSC file is not available during import, lines are imported in simple linetypes. After the import, the RSC file is not needed anymore. This method supports both V7 and V8 DGN files.

With this method you can work in AutoCAD with such linetypes as parallel lines, hatched double-lines, lines with special symbols at its ends, lines starting with one symbol and ending with another one, etc. - see an example:

As the standard mechanism for linetype definitions in AutoCAD (.LIN) does not allow to work with such types of complex lines, the DGN Import uses a special extension of standard drawing objects. The entities behave like normal lines and polylines but they are saved back to older AutoCAD versions as entities with proxy objects. These non-standard linetypes can be also assigned to other drawing objects.

We recommend to avoid grip-editing on polylines with these non-standard linetypes.